The invention relates to a method for the rounding of edges of an injection hole duct in a nozzle body and to a nozzle body for a fuel injection nozzle. Such a method and such a nozzle body are known from German Patent DE 195 07 171 C1.
A fuel injection nozzle is formed of essentially two parts, a nozzle body and a nozzle needle, the nozzle needle being inserted axially moveably in the nozzle body.
The nozzle body is generally configured cylindrically with an inner bore and, at its end located on a combustion space side, has a conically tapering dome region which is closed off by a blind hole. The nozzle needle carries, at its lower end, a sealing cone which, in a state of rest, is pressed onto a conical sealing face in the dome region of the nozzle body. Depending on the type of injection nozzle, at least one injection hole duct leads from the blind hole or the conically tapering dome region of the nozzle body, downstream of the sealing seat, through the nozzle body into the combustion space of an engine. When the moveable nozzle needle is lifted off with its sealing cone from the sealing seat in the nozzle body, the injection hole duct is exposed and fuel is injected in the combustion space.
In the nozzle body illustrated in German Patent DE 195 07 171 C1, the injection hole duct is configured as a rectilinearly continuous bore which is introduced in the nozzle body obliquely to the inner bore according to the desired injection hole cone angle. The result of the oblique orientation of the injection hole duct is that the fuel introduced into the inner bore with very high pressure has to be deflected sharply in order to be injected into the combustion space via the injection hole duct. This leads to a reduction in the fuel velocity and consequently to undesirable throttling of the fuel jet injected into the combustion space and, furthermore, a strength-reducing notch effect.
In order to achieve an improved fuel injection jet characteristic, German Patent DE 195 07 171 C1 proposes to round off, edgeless, the injection hole duct in the entry region at the transition into the sealing seat of the nozzle body, an upper entry region which faces the fuelflow direction having a larger rounding radius than a lower entry region which faces away from the flow direction. Despite the rounding off of the entry region, the fuel stream continues to be subjected, at the transition from the inner bore of the nozzle body into the injection hole duct, to a sharp deflection which markedly reduces the throughflow coefficient of the fuel stream and thus leads to injected fuel suffering flow-around and velocity losses. Furthermore, the limited throughflow coefficient of the fuel stream in the injection hole duct also restricts the throughflow quantity and therefore the volume injected into the combustion space of the engine.
It is accordingly an object of the invention to provide a nozzle body for a fuel injection nozzle with an optimized injection hole duct geometry that overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which ensure an improved injection jet characteristic.
With the foregoing and other objects in view there is provided, in accordance with the invention, a shape forming method, which includes, first providing a fuel injection nozzle having a nozzle shank with an inner bore formed therein and with a conically tapering dome region. The dome region has an injection hole duct formed therein and the injection hole duct is formed laterally into the dome region. The injection hole duct has an entry region being funnel-shaped with differently rounded-off edges. Second, there is the step of forming a degree of rounding of the edges of the entry region of the injection hole duct in dependence on a distribution of a fuel stream around the entry region. An edge portion of the entry region being more rounded a greater the fuel stream is at the edge portion.
In accordance with an added feature of the invention there are the steps of determining the distribution of the fuel stream around the entry region of the injection hole duct by a simulation calculation; and carrying out the degree of rounding of the edges of the entry region on a basis of the simulation calculation.
In accordance with an additional feature of the invention, there is the step of carrying out the degree of rounding of the edges of the entry region of the injection hole duct by hydroerosive grinding.
According to the invention, the edges at an injection hole duct in a nozzle body are rounded in such a way that the degree of rounding of the edges of the entry region is coordinated with the distribution of the fuel stream around the entry region. The edge portions being the more rounded, the greater the fuel stream at these edge portions is.
By this optimization of the entry region of the injection hole duct, the deflection angle, which results from the alignment of an inner bore and a seat cone in the nozzle body and a desired injection angle in a combustion space of an engine, is reduced to a minimum. As a consequence of which the throughflow coefficient of the fuelflow and therefore the velocity of the fuel injected out of the injection hole duct into the combustion space can be increased. Moreover, by the reduced deflection angle, turbulences in the fuel are also reduced as far as possible, so that the injection jet acquires an optimized flow profile.
According to the invention, the entry region of the injection hole duct in the nozzle body has essentially the form of an ellipse. A major axis of the ellipse coinciding with a direction of the fuelflow through the inner bore of the nozzle body, and the edges of the entry region being more rounded in a vertex region of the major axis of the ellipse than in the vertex region of a minor axis of the ellipse. This embodiment of the entry region of the injection hole in the nozzle body ensures an optimized fuel deflection, with the result that undesirable turbulences in the injected fuel and throttling of the flow velocity are prevented.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a nozzle body for a fuel injection nozzle, which includes a nozzle shank having an inner bore formed therein and a dome region with at least one injection hole duct formed therein. The dome region has an entry region leading into and defining an entry of the at least one injection hole duct. The entry region has differently rounded-off edges and the injection hole duct being a substantially ellipse shaped injection hole duct with a minor axis and a major axis coinciding with a direction of fuel flow through the inner bore of the nozzle shank. The edges of the entry region being more rounded in a vertex region of the major axis of the ellipse shaped injection hole duct than in a vertex region of the minor axis of the ellipse shaped injection hole duct.
In accordance with an added feature of the invention, the entry region has a form of a degenerate ellipse. An edge in the vertex region of the major axis of the degenerate ellipse facing the inner bore of the nozzle shank is more rounded than an edge in the vertex region of the major axis facing away from the inner bore of the nozzle shank.
In accordance with another feature of the invention, the edges of the entry region are rounded in a range of 10 xcexcm to 70 xcexcm.
In accordance with a concomitant feature of the invention, the entry region includes a first entry region part, a second entry region part and a third entry region part. A degree of rounding of the edges of the entry region, as a percentage, is defined as follows:
rounding of the first entry region part=[Dxc3x97(30 to 40)]/Sxc3x97100;
rounding of the second entry region part=[Dxc3x97(10 to 20)]/Sxc3x97100; and
rounding of the third entry region part=[Dxc3x9725]/Sxc3x97100;
where D corresponds to a hydraulic throughflow through the nozzle body after a rounding and S to a number of injection holes.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a nozzle body for a fuel injection nozzle with an optimized injection hole duct geometry, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.